1. Field of the Invention
The present invention relates to a display device, and more particularly, to a liquid crystal display device and a method for manufacturing the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for preventing a touch defect, and a method for manufacturing the same.
2. Discussion of the Related Art
The development of information-dependent society has increased the demand for various types of display devices. To fulfill the demand, efforts have been made to research flat panel display devices, such as a liquid crystal display (LCD) device, a plasma display panel (PDP), an electro-luminescent display (ELD), and a vacuum fluorescent display (VFD). Some of these flat panel display devices are being practically applied in various display purposes.
Among the above mentioned display devices, LCD devices have been used as a substitute for cathode ray tubes (CRTs) because they have advantages of superior picture quality, light weight, thin profile, and low energy consumption. Thus, LCD devices are currently the most widely used type of flat panel display device. Various applications of LCD devices are being developed in association with not only mobile image display devices, such as monitors of notebook computers, but also in the monitors of televisions, which receive and display broadcast signals. Successful application of such LCD devices to a diverse group of different types of image display devices depends on whether or not the LCD devices can realize high picture quality, including high resolution, high brightness, large display area, and the like, while maintaining the characteristics of light weight, thin profile, and low power consumption. Hereinafter, a related art LCD device will be explained in reference to FIGS. 1 to 3.
FIG. 1 is an exploded perspective view illustrating an LCD device according to the related art. As shown in FIG. 1, the LCD device includes a first substrate 1 and a second substrate 2 bonded to each other such that a gap is defined between the first and second substrates 1 and 2. The LCD device also includes a liquid crystal layer 3 sealed in the gap between the first and second substrates 1 and 2.
The first substrate 1 of the LCD device in FIG. 1 includes a plurality of uniformly spaced apart gate lines 4 arranged in a first direction and a plurality of uniformly spaced apart data lines 5 arranged in a direction perpendicular to the first direction of the gate lines 4. The gate lines 4 and data lines 5 define pixel regions P. The first substrate 1 also includes pixel electrodes 6 arranged in each of the respective pixel regions P, and thin film transistors T respectively formed at each crossing of the gate lines 4 and data lines 5. Each thin film transistor T transmits a signal from an associated one of the data lines 5 to an associated one of the pixel electrodes 6 in accordance with a signal from an associated one of the gate lines 4.
The second substrate 2 of the LCD device in FIG. 1 includes a black matrix layer 7 for blocking light through regions of the second substrate 2 other than the pixel regions P. The second substrate 2 also includes red R, green G, and blue B color filter layers 8 respectively formed at regions corresponding to the pixel regions P for expressing red, green and blue color tones. A common electrode 9 is formed to cover the color filter layers 8 for controlling an electric field across the liquid crystal layer 3 together with the pixel electrodes 6.
In each pixel region P, liquid crystal molecules of the liquid crystal layer 3 interposed between the first and second substrates 1 and 2 are oriented in accordance with the electric field generated between the associated pixel electrode 6 and the common electrode 9. The amount of light passing through the liquid crystal layer 3 corresponds to the orientation degree of the liquid crystal molecules of the liquid crystal layer 3,. Thus, a corresponding image can be expressed by controlling the orientation of the liquid crystal molecules of the liquid crystal layer 3 in each of the pixels P. Such an LCD device is called a “twisted nematic (TN) mode LCD device”. A TN mode LCD device has the drawback of having a narrow viewing angle. However, an in-plane switching (IPS) mode LCD device has been developed to overcome this drawback of the TN mode LCD device.
In the IPS mode LCD device, a pixel electrode and a common electrode are formed on a first substrate in each pixel region of the first substrate such that the pixel electrode and common electrode extend parallel to each other. An in-plane electric field (i.e., horizontal field) can be generated between the pixel electrode and a common electrode. The orientation of the liquid crystal molecules of the liquid crystal layer is controlled by the in-plane electric field.
To maintain a uniform cell gap for the liquid crystal layer, spacers are provided between the first and second substrates of the LCD devices having the above described configurations. The spacers are classified into either ball spacers or column spacers depending on their shape. The ball spacers have a spherical shape, and are scattered between the first and second substrates. Even after the first and second substrates are bonded to each other, the ball spacers are free to move about in the liquid crystal layer. Further, the ball spacers have a small contact area with respect to the first and second substrates. On the other hand, the column spacers are formed during an array process of either the first or second substrate. The column spacers are affixed on one of the substrates. Further, the column spacers have a cylindrical shape with a certain height to maintain the cell gap. Accordingly, the column spacers have a relatively large contact area with respect to the first and second substrates as compared to the ball spacers.
FIG. 2 is a plan view illustrating a related art LCD device including column spacers. FIG. 3 is a cross-sectional configuration view taken along line I-I′ of FIG. 2. As shown in FIGS. 2 and 3, an array region of the related art LCD device includes a plurality of gate lines 4 and data lines 5 arranged perpendicular to each other to define pixel regions, thin film transistors (TFT) formed at each of the crossings of the gate lines 4 and data lines 5, and pixel electrodes 6 formed in each of the respective pixel regions. The related art LCD device also includes column spacers 20 for maintaining the cell gap. FIG. 2 illustrates that three sub pixels, more particularly, R, G, and B sub pixels, constitute one pixel, and each pixel is provided with one column spacer 20.
Referring to FIG. 3, each column spacer 20 is formed at a corresponding position over the associated gate line 4. Specifically, the gate line 4 is formed on the first substrate 1, and then, a gate insulation film 15 is formed over the entire surface of the substrate 1, including the gate line 4. Thereafter, a passivation film 16 is formed over the gate insulation film 15.
The second substrate 2 includes the black matrix layer 7 for covering non-pixel regions (regions corresponding to gate lines, data lines, and thin film transistors) other than the pixel regions, and the red R, green G, and blue B color filter layers 8 formed over the color filter substrate 2, including the black matrix layer 7. The red R, green G, and blue B color filter layers 8 are formed by applying red, green, and glue pigments to regions of the substrate 2 corresponding to the respective pixel regions in sequence. The second substrate 2 also includes a common electrode 14 formed over the entire surface of the second substrate 2, including the color filter layers 8. After the column spacer 20 is arranged over the common electrode 14 at a position corresponding to the gate line 4, the two substrates 1 and 2 are then bonded to each other such that the column spacer 20 is located over the gate line 4.
In the above described related art LCD device having the column spacer 20, if a surface of the LCD device is touched with a finger or object along a certain direction, a spot is generated at the touched portion. The spot may be called a “touch spot” because it is generated by a touch action, or may be called a “touch defect” because it is observed on the screen where a touch occurred. The reason why the touch defect occurs in the LCD device having the column spacer 20 is that the column spacer 20 and the first substrate 1 facing the column spacer 20 have a large contact area as compared to the related art ball spacer, resulting in a large frictional force causing the touch defect. That is, since the column spacer 20, having a cylindrical shape, has a larger contact area with the first substrate 1 than a ball spacer, when first and second substrates 1 and 2 are shifted relative to each other by a touch action, the large frictional force of the larger contact area prevents a return to their original state, resulting in generation of long-lasting spots.